Monitoring Spawning Activity of Japanese Red-Bellied Newts, Cynops pyrrhogaster (Amphibia: Salamandridae), Using Artificial Egg Strips

Spawning activity of the Japanese red-bellied newt, Cynops pyrrhogaster, was surveyed in Minami-ohsawa, Hachioji-shi, Tokyo, using artificial egg strips. The number, size, and mortality of the deposited eggs were monitored daily from April to July in 2017. Spawning activity was observed mainly over three months from April to June, and a total of 5,339 eggs were successfully detected using artificial egg strips, which was estimated to be approximately 40% of the total number of eggs deposited in the study population. Time-series data were analyzed using state-space modeling to estimate the impact of water temperature on spawning parameters owing to the presence of plausible temporal autocorrelation. The survey quantitatively showed seasonal changes in spawning activity and demonstrated a significant effect of water temperature as females laid more eggs on warmer days. The average daily mean egg size was 2.19 mm (SD=0.05, N=86), and average daily egg mortality was 0.169 (SD=0.148, N=84), with clear seasonal trends: a convex trend for egg size and a concave trend for egg mortality. We did not detect any significant effects of water temperature on egg size or mortality. Currently, there are no data on the factors affecting seasonal changes in egg size and mortality in this species. Newt eggs are difficult to find in natural ponds, but the present study demonstrated that newt surveying using artificial egg strips is an effective way to monitor newt spawning activity.